1. Field of the Invention
The present invention generally relates to a method and system for calibration, in particular, to a method and system for calibrating laser measuring components.
2. Description of Related Art
In the field of computer graphics, three-dimensional (3D) model construction has been extensively applied in aspects such as industrial design, reverse engineering, medical image processing, criminal identification, digital documentation of culture artifacts, archaeological artifacts Geometric measurement techniques in measuring the contour shape of an object are mainly classified into contact measurement and non-contact measurement.
The contact measurement technique is frequently applied in industrial engineering thanks to its precision. However, such method involves point-by-point scanning through an object surface, which may be inefficient and may potentially destroy the object. Therefore such method is not suitable for reconstructing culture artifacts or archaeological artifacts. On the other hand, the non-contact measurement technique involves emitting energy onto an object and detecting its reflection in order to calculate the 3D data of the object.
One of the most commonly adopted non-contact measurement methods is triangulation. In a triangulation based measurement approach, a laser measuring apparatus projects a laser light beam onto the surface of an object, and a camera is exploited to look for the location of a laser dot on the object, where the laser dot, the camera, and the laser measuring apparatus form a triangle. As the distance between the laser measuring apparatus and the object changes, since the distance between the laser measuring apparatus and the camera as well as the angle of the laser light beam emitted by the laser measuring apparatus are known, the distance between the object and the laser measuring apparatus may be calculated based on the location of the laser dot in the camera's field of view. Such approach is more precise and is adapted for examining circuit boards in the field of precision molding technology or semiconductor electronic technology. Moreover, in some existing cases, a single laser dot may be substituted by a slit laser which is able to be swept across the object to speed up the measuring process.
In terms of a conventional laser measuring apparatus such as a laser measuring apparatus 100 in FIG. 1, it includes an image capturing unit 110 and a laser illumination unit 120. The image capturing unit 110 may be a camera with charge coupled devices (CCD), and the laser illumination unit 120 may be a linear light source. The angle between the central axis of an emitted laser beam and the viewing axis of the image capturing unit 110 is fixed. When an object A is disposed in front of the laser illumination unit 120 and the image capturing unit 110, a slit laser beam M may be projected onto the object A and captured by the image capturing unit 110.
However, since the distance between an object and a laser measuring apparatus may vary, the slit laser beam projected onto the object may result in different offsets. Hence, the performance of the laser measuring apparatus is dependent upon the accuracy of the calibration. Accordingly, to provide a method for calibrating the aforementioned laser measuring apparatus with simplicity and precision is one of the tasks to be solved.